This application claims priority under 35 U.S.C. § 119 to German Patent Application No. DE 102 005 060 129.4, filed Dec. 16, 2005, the entire disclosure of which is herein expressly incorporated by reference.
The invention relates to a method of controlling an onboard power supply system in a motor vehicle having a multi-voltage generator which supplies at least a first and a second partial power supply system each having several electric consuming devices, the first and the second partial power supply system having a first and a second voltage respectively and being mutually coupled by way of a parallel connection consisting of a voltage converter and a longitudinal controller.
Onboard power supply systems for motor vehicles developed in recent years having a second voltage level in addition to a first voltage level for supplying different consuming devices by way of a supply system. In these systems the first and the second voltage levels are mutually coupled by way of a voltage converter. Consuming devices with a low power consumption are connected to the first partial power supply system with the lower nominal voltage (e.g., 14 volts), and high-power consuming devices, (such as heaters, an electric power steering system, electromotive brakes, etc.) are connected to the second partial power supply system with the higher nominal voltage (e.g., 42 volts). In critical operating situations (for example, a surge operation), low-voltage consuming devices can optionally be supplied from the second partial power supply system.
The two partial power supply systems are supplied with electric power by a generator, such as a multi-voltage generator (MVG) which, depending on the voltage applied to its exciting coil, generates a high or a low voltage. While the generator supplies the partial power supply system with a higher or variable voltage directly, the supply to the partial power supply system with the low voltage takes place by a regulated voltage (DC-DC) converter. When the supplying the partial power supply system with a high or variable voltage is no longer required, the generator is regulated back to the lower voltage of the second partial power supply system and the voltage converter is connected.
The construction and manufacturing of voltage converters require high expenditures, and the required components, such as filter capacitors and battery supply coils, are not suitable for high temperatures. In addition, measures have to be taken for the interference suppression because high currents with very steep edges are switched in DC-DC converters. The size of the DC-DC converters has to be designed for a maximal power, although the maximal power needs to rarely be switched in a motor vehicle.
One solution is to provide a longitudinal controller parallel to the voltage converter in order to relieve the DC-DC converter and therefore allow it to be smaller and more cost-effective. Longitudinal controllers are robust and have a high temperature resistance. They can be cooled by means of the engine cooling water, and their interference emission is low.
Such a construction is disclosed in German Patent Document DE 102 62 000. This document discloses an onboard power supply system for a motor vehicle having at least a first and a second voltage level and a generator, the first and the second voltage level being mutually coupled by way of a first coupling device and the first coupling device comprising a longitudinal controller. The onboard power supply system comprises a first regulating device which triggers the longitudinal controller while taking into account the future loading of the second voltage level.
However, during idling the problem arises that the generator provides only a little more power than a normal 14-volt generator. The power of the generator will rise until the maximal voltage or power has been reached only when the rotational speed is increased. Accordingly, because the power of the generator depends on the rotational engine speed all consuming devices cannot be simultaneously supplied in any operating condition of the vehicle.
The electric power therefore has to be distributed as intelligently as possible, while safety, legal regulations and comfort definitions have to be taken into account. In particular, this necessity becomes noticeable due to, for example, windshield heating devices. A windshield heating device comprising a vapor-coated foil cannot be operated at 14 volts because the resistance of the foil cannot be reduced arbitrarily. When the voltage is too low there is insufficient power and the defrosting function is limited. Although the generator can provide more power as a result of the additional degree of freedom of the variable voltage, the maximal power is also limited during the idling. A windshield heating device can therefore be operated only by use of an intelligent distribution of power due to the variable generator voltage in the range close to idling.
It is an object of the present invention to provide a method which ensures the optimal utilization of the offered electric power and, in particular, ensures the supplying of large consuming devices, such as the windshield heating device.
This oject is achieved by a method of controlling an onboard power supply system that assigns a separate priority to the several electric consuming devices of the first and second partial power supplies and supplies the electric consuming devices as a function of their respective priority in such a way that the sum of the consuming device powers does not exceed a defined power value of the generator.
The object according to the invention is achieved by creating an intelligent power distribution in which the individual consuming devices are provided with a supply priority. In other words, a “prioritization” is implemented. The basis of this prioritization is a momentary generator power, and this generator power is optimally distributed to the connected consuming devices.
The method according to the invention of controlling an onboard power supply system for a motor vehicle having a multi-voltage generator, which supplies at least a first and a second partial power supply system having, in each case, several electric consuming devices, the first and the second partial power supply system having a first or a second voltage and being mutually coupled by way of a parallel connection consisting of a voltage converter and a longitudinal controller, involves assigning a separate priority respectively to the several electric consuming devices, and supplying the electric consuming devices as a function of their respective priority, so that the sum of the consuming device powers does not exceed a defined power value of the generator.
In particular, one or several of the following characteristics are implemented:
An old consuming device is replaced by a new consuming device                if the priority of the old consuming device is below the priority of the new consuming device, and        the sum of the consuming device powers, including of the new consuming device, exceeds the defined power value;        
the power value of the generator corresponds to the momentary power of the generator;
the power value of the generator corresponds to the sum of the consuming device powers to the extent that the priority of the consuming devices is above a defined threshold priority, the generator power being raised by at least one of the following steps:                Boosting of the generator,        adapting the rotational idling speed of the engine, and        boosting the voltage converter;        
the priority of the consuming devices is dynamically determined as a function of driving and environmental parameters.
In this case, the boosting of the generator means that the latter is overloaded in the cold condition and the voltage is superelevated at the exciting winding of the generator. The adaptation of the rotational idling speed essentially raises the rotational idling speed in order to correspondingly increase the voltage of the generator. The boosting of the voltage converter is also achieved by an intentional overloading of the converter in the cold condition.
The invention has the advantage, among others, that the possibility is created of being able to electrically heat a windshield to which a vapor-coated foil is glued, even if the power output of the generator is at the lower limit. Furthermore, the interior can be heated more rapidly than by means of a heating/PTC technique according to the state of the art. In addition, when recuperative power is used for the catalyst heating, the vehicle occupant compartment heating, the windshield heating, and the conventional electric onboard power supply system is not loaded as much. As a result, the charging balance of the battery will improve with a simultaneous increase of the service life of the battery by a reduced cyclization. The air-conditioning comfort is also improved because a higher electric power is also available in the low rotational engine speed range. Safety is also improved because the windshield heating device is supplied while the comfort is very high.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.